Polyurethane coated substrate and method of coating



April 12, 1966 F. C. WEBER, JR

POLYURETHANE COATED SUBSTRATE AND METHOD OF COATING Filed Jan. 2, 1964POLYURETHANE PRIME COAT NCO to OH ratio less than ISOCYHNA TE PREPOLYMERLEHTHER POLYOL P01. YUR ETHA NE FIN/6H conr NCO to OH ratio greater than150C YEA/A TE PREPOLVMER P L YOL HIR DRY/N6 POLYURETHANE COATED LEATHER/NVENTOR.'

FPED C. WEBER JR.

TTORA/EYS United States Patent 3,245,827 POLYURETHANE COATED SUBSTRATEAND METHOD OF COA'HNG Fred C. Weber, Jan, Ciayton, Mo., assignor toPhelan- Faust Paint Manufacturing Company, St. Louis, M0.,

a corporation of Missouri Filed Jan. 2, 1964, Ser. No. 335,382 17Claims. (Cl. 117-76) This application is a continuation-in-part of myco-pending application Ser. No. 46 ,343, filed Aug. 1, 1960, forPolyurethane Coating for Leather, now abandoned.

This invention relates to improvements in leather and other substratecoatings, and, in particular, to a polyurethane coating of a specialformulation.

In the past leather finishes have been of two classifications, watersoluble finishes and organic solvent finishes. T he water solublefinishes have generally provided leather coatings of suitable flexingcharacteristics, but have been objectionable because of lack of waterresistance. On the other hand, the organic solvent finishes, althoughbeing usually of a high degree of water resistance, have had relativelypoor adhesion, poor flexibility, or undesirable tack.

Efforts have been made to improve the organic solvent finishes byemploying an organic polyisocyanate composition, as in the LoshaekPatent No. 2,884,340, granted Apr. 28, 1959. However, the lack ofcontrol using the composition and process of this patent makes itdifficult to provide a truly satisfactory coating in actual productiondue to reaction of the polyisocyanates with the leather chemicals, suchas lipids, amides, and amines, among others, which are undesirable andmay cause stiffening of the leather. As a special feature of the instantinvention, such reaction may be avoided by using a multi-finish coatingin which the ratio of isocyanate to OH bearing reactants is such thatinsufficient isocyanate is provided to react with the leather chemicalsin the prime coat and wherein the ratio is increased in the top coat toprovide an excess of isocyanate to eflect intercoat reaction andfacilitate intercoat adhesion.

Although the invention is herein described with respect to leather,other substrates such as cellulosic material, wool, nylon, glass fiberand the like may be employed. Such substrates have reactive groups thattend to react with the isocyanate as do the leather chemicals. Thus,cellulos-ic materials have OH groups, nylon has a polyamio'e group, andglass fiber has adsorbed moisture all of which may be reactive. Thus,although this invention is described with repsect to leather, it will beunderstood that other substrates may be employed wherever reactivity ofthe substrate with the isocyanate is a problem.

By means of the instant invention there has been provided a polyurethanecoating that is easy to apply, has a high degree of water resistance,and provides. a hard and durable coating that has exceedingly highflexibility. The coating is similar to the so-called patent leathers andin actual flex tests has been satisfactorily subjected to over onemillion flexing operations without failure, whereas the best of otherconventional coatings, including polyurethane coatings, have failed atas low as 120,000 flexings.

The improved polyurethane coating of this invention employs anisocyanate reacted with polyols of a particular type, i.e., polyestersor polyethers having a particular number of hydroxyl groups and aspecified functionality and molecular weight range.

The accompanying drawing is a flow sheet illustrating the method.

The polyols employed are linear polyols and branched polyols. The linearpolyol employed has a preferable molecular weight range of 2500 to 3000,although it may be as low as 2000 or as high as 5000, and afunctionality 3,245,827 Patented Apr. 12, 1966 .alkanolamines areemployed and may be as high as 1500 and the functionality may be as highas 4.0. It is another particular feature of this invention that thelinear polyol and the branch polyol above described may be used incombination and, particularly where polyesters are employed, the ratioof the branch chain polyol to the linear polyol can vary from 0 to 6parts to 1 part of the linear polyol on an equivalence basis. If thebranch polyol is used in an amount above 6 parts, it has been found thatcracking of the coating may occur as there is not enough of the linearpolyol. On the other hand, no branch chain polyol need be employed in aparticular embodiment of this invention where special proportioning ofthe components is followed. However, where a slight tack on anequivalence basis occurs it is desirable to use at least some branchpolyol, and, as an example, as low as onequarter part of the branchpolyol to one part of the linear polyol can be employed. At these lowproportions, or with the use of the linear polyol alone, it has alsobeen found that there is slightly less tack with the use of an aminecatalyst.

It is also a special feature of this invention to control the reactionof the polyol with the isocyanate in the prepolymer before theapplication to leather for the for-mation of the coating thereon. Thisis done by preparing a prepolymer mix of the isocyanate and a separatepolyol. In the preparation of this prepolymer mix at least about 10%excess of isocyanate to the polyol is employed, and this excess may beas high as as an example.

In determining the proportions of the branch polyol to the linearpolyol, it should also be noted that at the lower ratio of the branchpolyol, the abrasion resistance is generally poor. Likewise, there ispoo-r chemical resistance in the coating Where steam and solvents areencountered. On the other hand, at the higher ratio of the branch polyolto the linear polyol, as in the ratio of 6:1 to prevent cracking, thebranch polyol should be only slightly branched and of relatively lowfunctionality.

It is also a feature of this invent-ion that in the application of thecoating the isocyanate is added as a prepolymer preferably as a reactionproduct of a diisocyanate with a dior tri-functional polyol. Theprepolymer may have a molecular weight range of about 600 to 3500. Thetri-functional polyol is in the form of the branched polyol, having amolecular weight range of to 900. The difunctional polyol is preferablyin linear form, although some branching may improve solubility, and hasa molecular weight range of 500 to 3000 with the hydroxyl group as nearto the end of the chain as possible.

Among the polyols employed have been polyethers such as hydr'oxylcontaining ethylene and propylene glycols, as Well as tri-functionalpolyols made from ethylene oxide or propylene oxide adducts oftri-functional polyols or castor oil derivatives. Other polyols areconventionally made by reaction of the glycols above mentioned withadipic acid or maleic anhydride to provide polyesters that are hydroxylterminated. The production of such polyols in the form of polyesters iswell known in the art as shown in the Carleton Ellis Patent No.2,255,313, granted Sept. 9, 1941. The polyethers employed are alsoconventional and have the same chain characteristics and molecularWeight and functionality characteristics in general as the polyesters.These polyethers may be conventional stock polyethers conventionallyobtained from such manufacturers as Dow Chemical Company, Union CarbideCompany, and Wyandotte Chemical Company.

It has also been found that the isocyanate reaction can be promoted withpolysulfides, polyamides, or polyamines,

xylene, toluene, methyl ethyl ketone, methyl isobutyl ketone, ethylacetate, butyl acetate, phenyl acetate, and methyl Cellosolve acetatecan be employed. The aromatics are used because of their low cost, whilethe ketones are a true solvent for the polyols and the isocyanate andhave a limited boiling point range. The methyl Cellosolve acetate has asomewhat higher boiling point range. The solvent amount employed isnon-critical and can be in the general range of 2575% of thecomposition. In addition, ethyl acetate can be employed as a carrier forthe pre-polymer composition and the solvency properties of the ethylacetate can be used to vary viscosity.

Additionally, it has been found preferable to use a cellulose acetatebutyrate with the linear polyester. This agent is a solid, but is usedas a 10% toluene solution, as an example, for ease in handling. Thetoluene solution is not critical and other solvents can be used Wherethey are of proper compatibility. The employment of the celluloseacetate butyrate solution is made as a flow control to eliminatecrawling or cratcring of the composition and to cont-r01 viscosity. Inaddition, a silicone and other additives can be similarly employed.These components are used since the linear polyester is liquid andcontrol of the fluidity and viscosity is desired for proper applicationand penetration control. In some instances, it may be further noted thata nonionic oil or solvent miscible wetting agent can be used in theformulation for modification of the surface tension and to wet theleather and eliminate crawl and formation of craters and pin holes.

The basic reaction for the formation of the polyurethane is-the reactionof an isocyanate with the hydroxyl group of a polyester or polyether.This basic reaction is as shown below where R indicates a polyester orpolyether and RNCO is an isocyanate:

The particular isocyanate employed is preferably a difunctionalisocyanate, although a tri-functional isocyanate can be employed withsomewhat less desirability and somewhat less flexibility. As an example,the diisocyanate soorrOorn C2H5O(CH2OH)3 CHZOCNHOCER NCO 011301120CHzOCNHOCHa ornocunOom ,cyanate with the leather chemicals.

It is noted that in the above reaction the trir nethylol propane, usedas a polyol in the prepolymer formation, is all used up so to speak toreact with three of the NCO groups in the original isocyanate in theformation of the prepolymer, which prepolymer has additional NCO groupsavailable for further reaction with additional polyol of a differenttype as a polyester or polyether which is subsequently added at the timeof formation of the prime coat or the finish coat as the case may be.

In this invention a very durable flexible and hard coating can beachieved by a multiple application. This coating may be applied uponconventional leather commonly used in the shoe industry by variousmethods of application, the most practical and successful being byspraying. In the application, conventional pigments and soluble dyes canlikewise be advantageouslyincorporated without any difficulty. Theleather employed may be degreased full-grain leather for bestappearance, but buffed and nondegreased leather may also be employed.Split leather may also be employed.

To illustrate this invention, there will be described below severalexamples showing various formulations that can be employed. In the firstof these examples, it will be noted that in the prime coat, which isfirst laid down upon .the leather, an excess of polyol is employed overthe isocyanate, While in the finish coat an excess of isocyanate isemployed over the polyol. The excess of polyol in the prime coat avoidsthe possibility of reaction of the iso- The leather that is obtainedfrom conventional sources varies, as is well known in the art, in pHfrom 4 /2 to 6. The possibility of reaction of the isocyanate withlipids, amides, amines, and other chemicals, can, accordingly, beobviated by the proportioning employed in this invention. Thus, the veryreactive isocyanate, by the use of an excess of polyol, is madeunavailable to react with the leather chemicals and is not required forbonding with the polyol employed in a finished coat.

By the formulation first described, applicant has made possible thebonding of a prime coat directly to a finished coat. The isocyanate isemployed in both coats. No special preliminary leather conditioningcoating or intermediate coat is required to provide for adhesion to theleather or between the prime and finished coats.

EXAMPLE 1 In this example a prime coat and a finish coat are employed.In the prime coat, as well as in the finish coat, the isocyanateprepolymer is prepared separately from the polyol solvent blend byinterreacting an isocyanate like toluene diisocyanate with a polyol liketrimethylol propane. In the formulation, the polyol blend, which ispigmented, is identified as a polyol catalyst or resin phase, and theisocyanate prepolymer is identified as the prepolymer phase.

Primer coat Polyol catalyst phase: Percent by weight Long chain linearpolyester functionality 2.0

In the polyol catalyst phase the non-ionic oil or solvent misciblewetting agent acts to wet the leather and change the surface tension toeliminate crawl and prevent the formation of craters or .pin holes inthe leather. The wetting agent may be polyethylene glycol 400monol-aurate, soya lecithin, or the commercial embodiment of non-ionictritons. The solvents in the polyol catalyst phase are not critical andcan be adjusted as desired. The methylethyl ketone is a solvent for thesystem and is mor volatile than the toluol and is desired for betterpenetration control. However, it should not be used exclusively as asolvent since too much of the methylethyl ketone in the system willcause soaking into the leather to an undesired degree. The toluol is adesirable diluent and partial solvent for the system and is used in thenature of an extender. In the blending of the polyol catalyst phase andpro-polymer phase, four parts of polyol catalyst phase is used to onepart of prepolymer phase by volume in the prime coat. This correspondsto 83 parts of polyol catalyst phase to 17 parts prepolymer phase byweight. However, in practice, volumetric blending is desired as it ismore convenient for plant handling than weighing.

Finish coat Prepolymer phase:

Trifunctional isocyanate prepolymer (mol. wt. 970, functionality 3.0)Ethyl acetate as solvent Methyl isobutyl ketone as solvent In the finishcoat it will be noted that the polyester employed in the polyol catalystphase can be identical with the polyester employed in the prepolymerphase of the prime coat. The oil soluble aniline dye can be of anyproper type as the formulation is not critical. The cellulose acetatebutyrate has been found to be very important in this formulation. It isdiflicult to find a component that is compatible with the system, butcellulose acetate 'butyrate has worked extremely well. In the celluloseacetate butyratethe free hydroxy groups on the compound react with theisocyanate and provides a full control in viscosity to a desired degreeto keep down the penetration. In further formulations listed below, itwas formerly the practice to employ an intermediate swab coat betweenthe prime coat and the finished coat, but, by virtue of the instantformulation, this can very desirably be obviated with savings of laborand expense by the use of the cellulose acetate butyrate in the polyolcatalyst phase of the finish coat, as this component keeps the finishcoat from soaking in undesirably.

It will be noted in the finish coat that the prepolymer phase isidentical in formulation to the prepolymer phase of the prime coat. Thismakes the blending in manufacture quite convenient. In'the blending ofthe polyol catalyst phase and the prepolymer phase of the finish coat,the two can be added together in equal quantities by volume. By weightthis corresponds to 52.6 parts of the polyol catalyst phase and 47.4parts of the prepolymer phase.

In the above formulation, the prime coat has a desirable NCO to OH ratioof 0.98 for best results. This, however, may be varied to as low as 0.5,but at this lower limit the prime coat is somewhat tacky and difficultto handle. This may be compensated for to some extent by employing arelatively greater vNCO to OH ratio in the finish coat. Theratio mayalso be increased to 1.25, but at this higher value there is inferiorintercoat adhesion because of some possible reaction of the isocyanatewith the leather chemicals and moisture in the air. In the finish coatthe NCO to OH ratio is preferably 2.1. For the excess NCO, excess polyolin the prime coat and moisture from the air will complete the curing ofthe isocyanate in the finished coat. The NCO to OH ratio in the finishcoat, however, may be as low as 1.1, but at this low ratio and with theparticular polyester employed there is a tackiness present unless ahigher functionality polyester is employed, such as a trifunctionalpolyester, to increase cross linking. However, this should be balancedbecause flexibility will be decreased. The ratio may also be as high as2.5, but at this higher ratio the coat will tend to be too inflexiblebecause of higher cross linkage. However, where the basic leather is toostretchy and pull up is high, the high ratio of NCO to OH of 2.5 to 1and even higher may be utilized to make the leather less stretchy andmore uniform. Thus, as an example, the NCO to OH ratio in such cases maybe as high as 3.7 to 1.

In the prime coat, as previously mentioned, the NCO moiety in thediisocyanate p-repolymer to the OH moiety in the polyol should be about.5 up to about 0.99 or slightly less than 1 to 1 to prevent reaction ofthe NCO moiety with the leather chemicals with adverse results. Themajor portions and predominant portion of the OH moiety is from thepolyol and in most cases the NCO to OH ratio can be designed byreference to the polyol component. In some cases, however, in the polyolphase,

' solvents such as methyl isobutyl ketone, and other solvents employed,may be of varying purity, and there may be a substantial proportion ofalcohol and water both supplying an OH moiety. In such cases where theOH component is increased by addition of components other than thepolyol, the general overall NCO to OH ratio is depressed. It is afeature of this invention that the NCO to OH ratiois calculated on thebasis of the entire system, and in such cases where an appreciable OHmoiety may be present from other sources as well as the polyester, theOH effect of the solvents, and any other OH bearing components, shouldbe calculated into the system. This can be done very simply by figuringthe OH number of the solvent by conventional means, as most commercialsolvents have a known OH number. In such instances the NCO to OH ratiobased on the NCO moiety in the isocyanate prepolymer to the OH moiety inthe polyol only may be slightly greater than 1, since there isadditional OH in the solvent system which will bring the NCO to OH ratioin the complete system to a slightly less than a l to 1 ratio inaccordance with the aforementioned discussion. The examples that followare primarily based on an NCO to OH ratio calculation considering the OHand the polyol only, as the effect of the OH in the other solvents andother components employed is somewhat minimal. However, in Example 7 theOH ratio in the solvents is appreciable and is taken into considerationshowing the effect of a substantial amount of OH components in suchsolvent systems.

In the application of the formulation, the polyol catalyst phase isadded to the prepolym-er phase in the prime coat, together with mixing,shortly before application to the leather. The period of time for useafter mixing may be up to about 24 hours or so, but beyond that timesetting may take place and longer periods should be avoided. Theapplication of the prime coat may be made directly to leather to insurea good wet coat and complete covering of the leather. After theapplication of the prime coat and after drying, which may take place inabout 12 to 16 hours at F., or 6 to 8 hours at F., the

finish coat may be added to the prime coat. The finish coat may be mixedtogether in the same fashion as the prime coat as described above. Thefinish coat is then applied on top of the prime coat to insure completecoverage and wetting. The leather is then permitted to dry in air for asufiicient time to insure curing of the isocyanate. Where desired, fortop quality, an additional finish coat can also be employed by a secondapplication.

In the above formulation of Example 1, the prime coat is pigmented anddye may be employed in the finish coat. This provides a high degree ofuniformity and hold-out on nonuniform leather. Thus, it is possible touse leather of comparatively poor grade and obtain very desirablecoating results. The pigmentmakes it possible to make the appearance ofthe leather more uniform. It will be noted that carbon black may beemployed as the sole pigment where desired, and, if so used, thequantity should be as much as three to ten percent of the dry film. Athigher percentages there is a tendency to crack and at lower percentagesthere is a tendency not to fill all of the leather pores. Other pigmentsbesides barium sulfate can be employed in the prime coat. Where highbulk value pigments like barium sulfate are employed, a rather highweight percent is utilized as shown in the example. This can be 20 to50% of the total non volatiles in the coating, but lesser amounts can beemployed for pigments of lower bulking values than the barium sulfate.Use of pigments other than carbon black make it possible to produce anydesired color on the finished leather.

There are listed below several alternative formulations for theemployment of polyester as the polyol in the primer formulation toillustrate the breadth of the invention.

EXAMPLE 2 Polyol catalyst phase: Percent by weight Prepolymer phase:Percent by weight Isocyanate prepolymer (mol wt. 970, functionality 3.0)45.0 Ethyl acetate 15.0 Methyl isobutyl ketone 40.0

In Example 2 polyol catalyst phase and prepolymer phase are combined inthe volumetric ratio of 4 parts of polyol catalyst phase to 1 part ofprepolymer phase; In this formulation the N80 to OH ratio is 0.47.

In Examples 1 and 2 above, the linear polyester may be employed in thegeneral molecular weight range of 900 to 3000. However, at the lowerrange the formulation may tend to be too tacky, while at the higherrange it may be too insoluble. This may be compensated to some extent bymaking the lower range molecular Weight polyester of a higher degree ofbranching and slightly increasing the functionality, while at the higherrange the polyester should be linear and of relatively lowfunctionality. In the above examples also, silica gel may be employed inthe finish coat in a range up to 10% by Weight on the dry film basis.This silica gel is preferably employed in the so-called solvent. orcatalyst phase, i.e., the component that does not contain the isocyanateprepolymer. The lower percentages of silica gel will provide a fullgloss while at the high range the appearance Will be dead flat. It hasbeen found that 5% of silica gel is preferable and will provide a veryhigh degree of a chain with varying degrees of branching.

toughness, scuff, and abrasion resistance, as well as a low lusterfinish, which is highly desired in mens shoes.

It has also been found that polyethers, as mentioned previously, may beused as the polyol. Thus, a polyether isocyanate repolymer can bedesirably employed. The polyethers may be cross linked with hydroxylbearing aminereactants, although other hydroxyl bearing agents may beemployed. Thus, as example, triethanolamine, triisopropanolamine, andmethyl diethanolamine may be employed. Likewise, quadrifunctional aminessuch as N,-N,N ,N ,-tetrakis (2-hydroxy propyl) ethylene diaminemanufactured by Wyandotte Chemical Company under the trademark Quadro-lmay be employed. In this reaction the amine portion acts as a catalyst.Where other hydroxyl bearing agents are employed, they may be in thenature of poly-glycols, trimethylpr-opane, which gives a rather slowreaction, and castor oil derivatives of varying types. Thequadrifunctional amines give the fastest reaction time and the greatestdegree of cross linking. In general, as the functionality of thealkanolamine increases, the NCO to OH ratio drops in order to producesatisfactory pot-life and film characteristics.

There are listed below several examples showing the use of polyetherprepolyrners. In the polyether isocyanate prepolyrners, polyetherglycols may be employed. Thus, diand trifunctional glycols can beutilized to form g I Basically the polyethers are linear with somebranching. The range employed may provide a molecular weight of 900 to3500 and at the lower molecular weight range of functionality of 2.5 isdesirable, while at the higher range a functionality of 2.0 ispreferable. It has been found that for best results a glycol having amolecular Weight of about 2590 to provide a reaction product with theisocyanate of molecular weight of 2800 and a functionality of 2 is verydesirable.

Variants in the polyether formulation illustrating the range thatcan beemployed are listed below. These variants show the range that can beemployed in the prime coat.

. Prepolymer phase:

Isocyanate polyether prepolymer (mol. Wt. 2800,

functionality 2.0) 65 Xylol 35 Polyol catalyst phase is added toprepolymer phase in the volumetric ratio of 1 part of polyol catalystphase to 4 parts of prepolymer phase. This provides an NCO to OH ratioof 0.9.

EXAMPLE 4 Prime coat Polyol catalyst phase: Percent by weight Quadrol25.7 Xylol 74.3

Prepolymer phase:

' Isocyanate prepolymer (mol. wt. 2800, functionality 2.0) 65 Xylol 35'9 Polyol catalyst phase is added to the prepolymer phase in thevolumetric ratio of 1 to 4. This provides an NCO to OH ratio of 0.6.

To illustrate variants in the formulation of the polyether finish coat,reference is made to Examples 5 and 6 below.

EXAMPLE 5 Finish coat Polyol catalyst phase: Percent by weight In thefinish coat the prepolymer phase is added to the polyol catalyst phasein a volumetric ratio of 4 parts of the prepolymer catalyst phase to onepart of polyol catalyst phase. This provides a weight ratio of 140 partsof the prepolymer phase to 52 parts of polyol catalyst phase. The NCOratio to OH is 1.5 to 1.

EXAMPLE 6 Finish coat Polyol catalyst phase: Percent by weight Castorpolyol (equiv. wt. 374) 33.8 Methyl diethanolamine 5.3 Xylol 22.4 MethylCellosolve acetate 38.5

Prepolyrner phase:

Isocyanate polyether prepolymer (mol. wt.

965, functionality 2.43) 82.5 Xylol 17.3 Oil soluble aniline dye 0.2

The above formulation is made by adding the polyol catalyst phase to theprepolymer phase in a 1 to l volumetric ratio. This provides an NCO toOH ratio when so combined of 1.26.

For the polyester and polyether isocyanate reaction products to providethe coatings listed above, very o'esirable characteristics have beenobtained. As an example, for the prime and finish coat laid down upon aglass plate to provide a 5 mil cast free film, it has been found that atensile strength of 2,000 to 3,000 p.s.i. can be obtained. Thischaracteristic is also obtained with an elongation of 100% andconsiderably higher elongations above 200% have been achieved. Likewise,the modulus is very desirable and at 100% is less than 200.

In Example 7 below a prime and finish coat are shown in which the OHcontent of components other than the polyols is appreciable and is takeninto account in calculating the desired NCO to OH ratio.

Prime coat Percent 0H NCO Wt. y equiv. equiv.

Weight POLYOL CATALYST rnnsn Barium sulfate- 991.2 Carbon black 42.8Iron blue 145. 9 Silicone 22. 7 Polyester (polyol, functionality 2.0)(MW 2000-3000) 1, 452. 9 Methylcthyl ketone solvenL. 797. 5 'loluolsolvent 374. 7

Total 3, 827. 7

PREPOLYMER rnnsn Methyl isobutyl ketcne 302. 8 40. 3 0. 0531 Prepolymer,functionality 3.0, mol wt. 970 449. 4 59. 7 1. 3009 Grand Total 4, 579.9

In this formulation the final finish coat is formulated by mixing 4parts of polyol catalyst phase to 1 part of the prepolymer phase all byvolume. The formulation provides an apparent NCO/OH ratio of 1.22:1 forthe isocyamate and polyol in the formulation. However, commercialsolvents are employed in this example having a substantial portion of OHbearing impurities and when their OH equivalence is calculated, thetotal OH in the system was found to have substantially increased. Whenthis effect was considered, the final NCO to OH ratio was found to be0.992: 1.

Finish Coat Percent OH NO 0 Wt. by equiv. equiv.

weight.

POLYOL CATALYST PHASE Polyester polyol, functionality 2.0 (mol wt. 2,0003,000) 1, 419. 4 62. 8 1.1132 Cellulose acetate butyrate 4. 2 2 0. 0049Butyl acetate solvent 496. 4 21. 9 0. 1655 Methyl isobutyl ketonesolvent 343. 1 l5. 1 0. 0602 Total 2, 263. 1 100. 0

PREPOLYMER PHASE Methyl lsobutyl ketone 841. 2 40. 2 0. 1476 Prepolymer,functionality 3.0 (mol Wt. 970) 1,248. 5 59. 8 3. 8041 Total 2, 089. 7100.0 1. 4914 3. 8641 Grand Total 4, 352. 8

In this formulation the finish coat is formulated by mixing 4 parts ofthe polyol catalyst phase to 5 parts of the prepolymer phase all byvolume. The final formulation provides an apparent NCO/ OH ratio of3.47111 for the isocyanate and polyol in the formulation. However,commercial solvents are employed in this example having a substantialportionv of OH bearing impurities and when their OH equivalence iscalculated, the total OH in the system are found to have substantiallyincreased. When this effect was considered, the final NCO to OH ratiowas found to be 2.598z1.

In the foregoing formulations the prepolymer is added to the remainderof the composition of the prime coat shortly before application to theleather. The period of time for use may vary, however, up to 24 hours,but beyond that time setting will take place and longer periods shouldthe avoided. In this application the linear polyester is liquid and thecellulose acetate butyrate is added as a 10% toluene solution, althoughother solvents also can be employed that are of proper compatibility, toprovide fiow control. Likewise, as mentioned previously, a

silicone can be used to increase the viscosity and to eliminatecrawling. To increase penetration, a nonionic oil soluble wetting agentcan also be employed. Dyes and pigments can be added. Dyes that are oilsoluble are preferred.

The prime coats, above described, after mixing and during the period oflife up to 24 hours or so, is then applied to the leather. Theapplication is made to insure a good wet coat and complete covering ofthe leather.

After 24 hours heat can be applied for pressing and other workingoperations subch as plating and the like.

After the application of the prime coat, there is a follow-up with theapplication of the finish coat. If desired, silica gel can be employedin the finish coat to provide a coating of superior abrasion, butsomewhat lower gloss. This provides a superior scutf resistance to thecoating. As an example, silica gel in the amount of 2 to 12% by weightof the finished coat composition can be employed and a preferable amountwould be 6% by weight for mens shoes, for example.

In the mixing of the prepolymer with the remainder of the composition inboth the prime coat and the finished coat, it should be noted thatthinning may be carried out to any desired degree by the properapplication of the solvents previously mentioned, since the amount ofthe solvent is not critical. The prepolymeris viscous whereas the linearpolyol used in the remainder of the composition is very fluid. To effectthe mixing of the prepolymer with the remainder of the composition, thetwo need merely to be added to one another accompanied by physicalmixing. This makes it very simple to use the composition in the factory,since up until the time of the application the prepolymer can be kept inone tank and the remainder of the composition can be kept in anothertank for long periods of time. It is only after the mixing that the lifeor" the composition is of importance, since, as previously mentioned,this mixed composition should be used within a 24-hour period.

The composition of the coating provided by the multiple coatapplications above described furnishes a urethane coating of a very highdegree of adhesion to leather. In addition, the coating is characterizedby high abrasion resistance and lack of tack coupled with a high degreeof gloss. The flexibility of the coating is likewise outstanding. Inactual tests the coatings have undergone flex tests in the order of2,000,000 operations without failure. As an example of comparison, othertypes of conventional urethane top coats have only withstood 120,000flexes, while ordinary leather withstood only 18,000. With linseed oilswablbing the leather withstood only 60,000 operations.

The leather coated with this composition can also be conventionallyworked upon by the usual factory techniques in preparing shoes and othertypes of leather. Thus, various plating operations and pressing can becarried out upon the coated leather with complete satisfaction. As anexample, a leather coated according to this composition, which wassubsequently plated, has withstood 600,000 flexes and showed no sign offailure at the completion of this test.

Accordingly, there has been provided a urethane coating of superiorqualities for application to leather. The coating is characterized byextremely high flexibility, a high degree of adhesion to the leatherthat resists peeling, as well as hardness and any degree of high as wellas low gloss. The composition and process of application is one thatwithout any complicated process controls can be conveniently employed inindustry with a high degree of success for its intended purpose.

Various changes and modifications, such as substitution of chemicalequivalents, may be made 'within this invention as will be readilyapparent to those skilled in the art. Such changes and modifications arewithin the scope and teaching of this invention as defined by the claimsappended hereto.

What is claimed is:

1. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of a prepolymer of anisocyanate with a polyol having at least one hydroxy group near itsterminal portion, said prepolymer having a molecular weight of about 600to 3500, and said polyol having at least one hydroxy group near itsterminal portion and a functionality of 2 to 4 and in which the NCO toOH ratio in the prime coat is about .5.98:1 and said finish coatconsisting essentially of the reaction product of a prepolymer of anisocyanate with a polyol having at least one hydroxy group near itsterminal portion, said prepolymer having a molecular weight of about 600to 3500 and said polyol having at least one hydroxy group near itsterminal portion and a functionality of 2 to 4 and wherein the NCO to OHratio in the finish coat is about 1.1-2.5 1.

2. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500, and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4 and in which theratio of the NCO to OH in the prime coat is about 0.5.98:1 and saidfinish coat consisting essentially of the reaction product of twocomponents, the first component being a prepolymer of an isocyanate witha polyol having at least one hydroxy group near its terminal portion,said prepolymer having an average molecular weight of about 600 to 3500and the second component being a separate polyol having at least onehydroxy group near its terminal portion and a functionality of 2 to 4and wherein the ratio of the NCO to OH in the finish coat is about1.1-2.5 :1.

3. The polyurethane coated leather of claim 2 in which the secondcomponent of the prime coat contains an oil miscible wetting agent.

4. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500, and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4 and in which theratio of the NCO to OH in the prime coat is about 05-9811 and saidfinish coat consisting essentiaily of the reaction product of twocomponents, the first component being a prepolymer of an isocyanate witha polyol having at least one hydroxy group near its terminal portion,said prepolymer having an average molecular weight of about 600 to 3500and the second component being a separate polyol having at least onehydroxy group near its terminal portion and a functionality of 2 to 4and wherein the ratio of the NCO to OH in the finish coat is about1.1-2.5:1, said finish coating containing up to about 10% silica gel toimpart lower gloss, added toughness and wear and scufif resistance tothe coating.

5. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500, and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4 and in which theratio of the NCO to OH in the prime coat is about 0.5-38:1 and saidfinish coat consisting essentially of the reaction product of twocomponents, the first component being a prepolymer of an isocyanate witha polyol having at least one hydroxy group near its terminal portion,said prepolymer having an average molecular weight of about 600 to 3500and the second component being a separate polyol having at least onehydroxy group near its terminal portion and a functionality of 2 to 4,and said finish coat containing cellulose acetate butyrate and whereinthe ratio of the NCO to OH in the finish coat is about 1.l2.5:1.

6 A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an excess .of a stoichiometricamount of isocyanate with a trifuctional polyol, said prepolymer havingan average molecular weight of about 600 to 3500, and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4, and a molecularweight of about 2,000 to 5,000, and in which the ratio of the NCO to OHin the prime coat is about 0.5- .98:1 and said finish coat consistingessentially of the reaction product of two components, the firstcomponent being a prepolymer of an excess of a stoichiometric amount ofisocyanate with a trifunctional polyol, said prepolymer having anaverage molecular weight of about 600 to 3500 and the second componentbeing a separate polyol having at least one hydroxy group near itsterminal portion and a functionality of 2 to 4 and a molecular weight ofabout 2,000 to 5,000, and wherein the ratio of the NCO to OH in thefinish coat is about 1.1-2.5: 1.

7. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500, and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4 and in which theratio of the NCO to OH in the prime coat is about 0.5-.9811, and an oilmiscible wetting agent in said second component, and said finish coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500 and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4, and wherein theratio of the NCO to OH in the finish coat is about 1.1-2.5: 1, saidfinish coating further containing cellulose acetate butyrate and up toabout 10% silica gel to impart lower gloss, added toughness and wear andscuff resistance to the coating.

8. A polyurethane coated leather comprising a leather substrate, apolyurethane prime coat and a polyurethane finish coat, said prime coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an excess of a stoichiometricamount of isocyanate with a trifunctional polyol and containing an oilmiscible wetting agent, said prepolymer having an average molecularweight of about 600 to 3500, and the second component being a separatepolyol having at least one hydroxy group near its terminal portion and afunctionality of 2 to 4, and a molecular weight of about 2,000 to 5,000,and in which the ratio of the NCO to OH in the prime coat is about0.5-.9821 and said finish coat consisting essentially of the reactionproduct of two components, the first component being a prepolymer of anexcess of a stoichiometric amount of isocyanate with a trifunctionalpolyol, said prepolymer having an average molecular weight of about 600to 3500 and the second component being a separate polyol having at leastone hydroxy group near its terminal portion and a functionality of 2 to4 and a molecular weight of about 2,000 to 5,000, and wherein the ratioof the NCO to OH in the finish coat is about 1.12.5:l, said finish coatfurther containing cellulose acetate butyrate and up to about 10% silicagel to impart lower gloss, added toughness and wear and scuff resistanceto the coating.

9. A method of applying a plurality polyurethane coating to leathercomprising a polyurethane prime and a polyurethane finish coating whichcomprises preparing a prime coating consisting essentially of thereaction product of a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving a molecular weight of about 600 to 3500 and said polyol having atleast one hydroxy group near its terminal portion and a functionality of2 to 4 and in which the NCO to OH ratio in the prime coat is about.5.98:1 and said finish coat consisting essentially of the reactionproduct of a prepolymer of an isocyanate with a polyol having at leastone hydroxy group near its terminal portion, said prepolymer having amolecular weight of about 600 to 3500 and said polyol having at leastone hydroxy group near its terminal portion and a functionality of 2 to4 wherein the NCO to OH ratio in the finish coat is about 1.1-2.5 :1,applying to said leather said prime coat, drying said prime coat andapplying at least one finish coat and drying the same.

10. A method of applying a plural polyurethane coating to leathercomprising a polyurethane prime and a polyurethane finish coating whichcomprises preparing a prime coating consisting essentially of thereaction product of two components, the first component being aprepolymer of an isocyanate with a polyol having at least one hydroxygroup near its terminal portion, said prepolymer having an averagemolecular weight of about 600 to 3500, and the second component being aseparate polyol having at least one hydroxy group near its terminalportion and a functionality of 2 to 4 and in which the ratio of the NCOto OH in the prime coat is about 0.5-.98:1 and said finish coatconsisting essentially of the reaction product of two components, thefirst component being a prepolymer of an isocyanate with a polyol havingat least one hydroxy group near its terminal portion, said prepolymerhaving an average molecular weight of about 600 to 3500 and the secondcomponent being a separate polyol having at least one hydroxy group nearits terminal portion and a functionality of 2 to 4 and wherein the ratioof the NCO to OH in the finish coat is about l.l2.5 :1, applying to saidleather said prime coat, drying said prime coat and applying at leastone finish coat and drying the same.

11. A polyurethane coated substrate comprising a substrate of leatherand the like, wherein said substrate contains material reactive withisocyanate, a polyurethane prime coat and a polyurethane finish coat,said prime coat consisting essentially of the reaction product of anisocyanate with a polyol having at least one hydroxy group near itsterminal portion and a functionality of 2 to 4 and in which the NCO toOH ratio in the prime coat is about 0.5 to 0.98:1 and said finish coatconsisting essentially of the reaction product of an isocyanate with apolyol having at least one hydroxy group near its termi nal portion anda functionality of 2 to 4 and in which the NCO to OH ratio in the finishcoat is in excess of 1:1.

12. The polyurethane coated substrate of claim 11 in which the NCO to OHratio in the finish coat is about 1.1-3.7:1.

13. The polyurethane coated substrate of claim 11 in which the NCO andOH ratio in the finish coat is about 1.1-2.5:1.

14. A method of applying a plural polyurethane coating to a substrate ofleather and the like, wherein said substrate contains material reactivewith isocyanate, said coating comprising a polyurethane prime and apolyurethane finish coating which comprises preparing a prime coatingconsisting essentially of the reaction product, an isocyamate with apolyol having at least one hydroxy group near its terminal portion, anda functionality of 2 to 4 and in which the NCO to OH ratio in the primecoat is about .5-.98:1 and said finish coat consisting essentially ofthe reaction product of an isocyanate with a polyol having at least onehydroXy group near its terminal portion and a functionality of 2 to 4wherein the NCO to OH ratio in the finish coat is in excess of 1:1,applying to said leather said prime coat, drying said prime coat andapplying at least one finish coat and drying the same.

15. The process of claim 14 in which the NCO to OH ratio in the finishcoat is about 1.1-3.7:1.

16. The process of claim 14 in which the NCO to OH ratio is about1.1-2.5:1.

17. A polyurethane coated substrate comprising a substrate of leatherand the like, wherein said substrate contains mate-rial reactive withisocyanate, a polyurethane prime coat and a polyurethane finish coat,said prime References Cited by the Examiner UNITED STATES PATENTS2,884,340 4/ 1959 Loshaek 11776 2,973,284 2/1961 Semegem 1l7-763,119,716 1/1964 Wooster 117-142 FOREIGN PATENTS 585,378 10/1959 Canada.815,185 6/1959 Great Britain.

OTHER REFERENCES Dombrow: Polyurethanes, Reinhold Pub. Co., 1957.

WILLIAM D. MARTIN, Primary Examiner.

MURRAY KATZ, Examiner.

1. A POLYURETHANE COATED LEATHER COMPRISING A LEATHER SUBSTRATE, APOLYURETHANE PRIME COAT AND A POLYURETHANE FINISH COAT, SAID PRIME COATCONSISTING ESSENTIALLY OF THE REACTION PRODUCT OF A PREPOLYMER OF ANISOCYANATE WITH A POLYOL HAVING AT LEAST ONE HYDROXY GROUP NEAR ITSTERMINAL PORTION, SAID PREPOLYMER HAVING A MOLECULAR WEIGHT OF ABOUT 600TO 3500, AND SAID POLYOL HAVING AT LEAST ONE HYDROXY GROUP NEAR ITSTERMINAL PORTION AND A FUNCTIONALITY OF 2 TO 4 AND IN WHICH THE NCO TOOH RATIO IN THE PRIME COAT IS ABOUT .5-98:1 AND SAID FINISH COATCONSISTING ESSENTIALLY OF THE REACTION PRODUCT OF A PREPOLYMER OF ANISOCYANATE WITH A POLYOL HAVING AT LEAST ONE HYDROXY GROUP NEAR ITSTERMINAL PORTION, SAID PREPOLYMER HAVING MOLECULAR WEIGHT OF ABOUT 600TO 3500 AND SAID POLYOL HAVING AT LEAST ONE HYDROXY GROUP NEAR ITSTERMINAL PORTION AND A FUNCTIONALITY OF 2 TO 4 AND WHEREIN THE NCO TO OHRATIO IN THE FINISH COAT IS ABOUT 1.1-2.5:1.